People with celiac disease experience a variety of gastrointestinal and, occasionally, extraintestinal symptoms when they consume gluten - the primary protein found in wheat. The biological mechanisms behind this autoimmune reaction are rather well understood, and the diagnostic tests for celiac disease are sensitive and specific. Similarly, people who are allergic to wheat experience a local or systemic allergic reaction when they come into contact with wheat-containing foods. The immunological reaction underlying a wheat allergy is the same as for other food allergies, and is similarly very well understood.
What is not well understood is the phenomenon of people who have neither celiac disease nor a wheat allergy, yet nonetheless experience digestive distress or extraintestinal symptoms when they consume wheat. Unlike the case of celiac disease or wheat allergy, proposed mechanisms behind this observed dietary intolerance have not been proven, nor have objective medical tests been identified and scientifically validated to diagnose the condition. Currently, a diagnosis is made by excluding autoimmune or allergic conditions in conjunction with clinical improvement of symptoms when wheat is eliminated from the diet. (Purported diagnostic tests for such sensitivity to gluten - including those with saliva, stool, hair or so-called "applied kinesiology" tests of muscle strength - are not supported by objective, peer-reviewed or replicable scientific data.)
All we can say for sure is that there's a significant number of folks out there who feel lousy when they eat wheat. According to nationally representative data, about half of one percent of all Americans followed a gluten-free diet in 2009 and 2010, but based on the proliferation of gluten-free products in the past several years and what I've seen in my practice, my guess is that number is already higher by now.
[Read: What is Gluten, Anyway?]
The term used to describe this symptomatic response to wheat, and to possibly other gluten-containing grains such as barley and rye, is "non-celiac gluten sensitivity." Of note, it has been observed that a significant percentage of patients with symptoms of NCGS also has irritable bowel syndrome. This makes me wonder: Is gluten really even the offender in some of these cases?
Wheat, barley and rye, like most foods, contain both protein and carbohydrates. Gluten - the main protein in these grains - gets most of the attention when we consider dietary intolerances. But these grains are also a significant source of a type of carb called a fructan. Fructans are essentially chains of fructose molecules that are very difficult to digest. You may recall meeting them in my previous articles on common triggers of IBS symptoms. They're one of several families of fermentable, poorly digested carbs we refer to as FODMAPs. In addition to wheat, barley and rye, other dietary sources of fructans include onions, garlic, artichokes, sunchokes, jicama and asparagus - all (gluten-free) veggies that are common triggers for gas, bloating and or diarrhea in a subset of patients with IBS. In other words, if you have IBS and have found onions and garlic to disagree with you, there's good reason to believe that fructan-rich grains might trigger symptoms as well, particularly when eaten in large portions.
This raises another question: What if NCGS isn't a gluten sensitivity at all - at least for some people - but rather a fructan sensitivity instead? What if non-celiac gluten sensitivity is really non-celiac fructan sensitivity?
Indeed, a recent study of people with IBS and NCGS suggested this very possibility. The researchers of this small but well-designed study gave participants a low-FODMAP diet, which was both wheat-free and gluten-free, for two weeks and noted an improvement in their digestive symptoms. Then, they challenged half the group daily with several grams of either isolated gluten (without the usual accompanying fructans) or isolated whey protein. There was no difference in symptoms experienced between participants in the respective groups, suggesting that among this set of people with IBS, gluten was no better or worse than another dietary protein in terms of provoking digestive symptoms in the context of an overall low-FODMAP diet. It would be interesting to see whether these results can be replicated in larger studies of people with IBS as well as others without the condition.
For most people who don't do well with wheat, the distinction between gluten and fructans may be an academic one, with little bearing on their day-to-day diet. After all, if wheat triggers symptoms, then it should be avoided - regardless of whether those symptoms are caused by a wheat protein or a wheat carbohydrate. Still, thanks to the wonders of modern food science, there are some cases in which a wheat-based food could be gluten-free but still high in fructans, ironically making it tolerable for a person with actual celiac disease but not for someone with NCGS.
For example, consider a new wave of beers that are brewed from malted barley but treated enzymatically to remove gluten. These beers have been testing below a threshold of less than 10 parts per million of gluten, rendering them technically gluten-free. (The Food and Drug Administration's threshold for labeling a food "gluten free" is less than 20 ppm.) But beer often contains some residual fermentable carbohydrates that may be digestively troublesome for sensitive folks even in the absence of gluten. The amount of residual, fermentable carbohydrate varies depending on the type of beer and the brewing process, with ales generally having the most and lagers having the least. The point is that these beers are an example of a food (or beverage, technically) that may be problematic for some patients with NCGS, but possibly not for those with celiac disease. As researchers push the frontiers of food science in an attempt to "detoxify" wheat flour from its gluten, it's possible we may one day encounter examples of gluten-free (but still high-fructan) wheat-based foods on a much more regular basis. Weird stuff!
The state of current knowledge into what we currently call NCGS is just the tip of what promises to be a very large iceberg. (And that iceberg may get a new name at some point as well.) Based on current research, it's possible that NCGS may turn out to be multiple distinct conditions - some resembling celiac disease with an underlying autoimmune cause triggered by gluten, some more typically allergic in nature and many just run-of-the-mill carbohydrate intolerances that got swept up the gluten-free frenzy. Stay tuned!
Tamara Duker Freuman, MS, RD, CDN, is a registered dietitian whose NYC-based clinical practice specializes in digestive disorders, celiac Disease, and food intolerances. Her personal blog, www.tamaraduker.com, focuses on healthy eating and gluten-free living.
Please note that the author cannot offer individualized medical advice to readers who contact her via email.